The major objective of this research project is to produce, extract, concentrate, identify, and test, for their ability to protectively immunize mice, antigens excreted and secreted by schistosomes in vitro. The specific aims are: 1. to identify the antigens in excretory and secretory products (exoantigens) of adult worms maintained in vitro; 2. to confirm the protective effect of immunizing mice with such exoantigens, and to investigate their role in protective immunity. Schistosomes are maintained in vitro by our methods for two weeks in a state comparable to that measured in vivo in mice. Rabbits and mice will be immunized with concentrated fluid or fluid fractions obtained from these cultures. Antibody production will be studied in immunized rabbits and mice, and protection in mice.